In the prior art several processes for the production of levulinic acid are described. Levulinic acid can, for example, be produced by acid catalyzed hydrolysis of C6 carbohydrate-containing feedstocks. The production of levulinic acid by acid catalyzed hydrolysis of C6 carbohydrate-containing feedstocks is described e.g. in WO2010/030617, US2010/312006, U.S. Pat. Nos. 5,608,105, 4,897,497 and 6,054,611.
Another process for the production of levulinic acid is a process that produces levulinic acid from furfuryl alcohol or its esters. An example of such a process is described in U.S. Pat. No. 4,236,021. Furfurylalcohol is converted at 125° C. to butyl levulinate in the presence of an alcohol, such as butylalcohol, with HCl as catalyst. Butyl levulinate is isolated via distillation. After hydrolysis in an aqueous environment levulinic acid is obtained.
A third process for the production of levulinic acid is from diethyl acetyl succinate as, for example, described in U.S. Pat. No. 5,189,215. Diethyl acetyl succinate can be made from diethyl maleate, which in general is derived from petrochemical based maleic acid anhydride.
In the present invention levulinic acid is produced by acid catalyzed hydrolysis of a C6 carbohydrate-containing feedstock. During acid catalyzed hydrolysis a solution is formed comprising levulinic acid and by-products (e.g. char, tar and angelica lactone) and a solvent.
The formation of char, tar and angelica lactone is a serious disadvantage of the production of levulinic acid by acid catalyzed hydrolysis. Char contains insoluble compounds which can be removed via traditional solid liquid separation steps such as decanting, filtering and other solid liquid separation technologies. Tar is composed of low to high-molecular weight oligomeric and polymeric compounds and other high boiling compounds. Tar can be soluble and/or partly insoluble. In particular tar forms a problem during the isolation of levulinic acid, for example during a distillation step. Liquid-liquid extraction is used in many processes according to the prior art. During the extraction of levulinic acid from the aqueous phase also a part of the tar is extracted. During distillation, that is needed for further purification, the remaining tar may accumulate in the distillation residue and forms a sticky, almost solid layer which is difficult to remove from the distillation column. The tar will foul reboilers and column internals and will make it very difficult to recover levulinic acid. The recovery of levulinic acid by distillation moreover often requires high temperatures and long residence times. Under these process conditions angelica lactone is formed via internal cyclisation and dehydration of levulinic acid.
Angelica lactone is the cyclic dehydration product of levulinic acid. It is also called 4-hydroxy-3-pentenoic acid γ-lactone or 5-methyl-2(3H)-furanone. Angelica lactone has a lower boiling point than levulinic acid and, thus will accumulate in the distilled levulinic acid fraction after removal of the tar. Angelica lactone may form colored compounds in the distilled levulinic acid fraction.
Here and hereafter, reaction product X is herewith defined as the reaction product that is directly obtained after the acid catalyzed hydrolysis of a C6 carbohydrate-containing feedstock.